Microwave sintered Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites for use in low temperature co-fired ceramics technology

The La3+ and Co2+ substituted Sr1-xLaxFe12-xCoxO19 (x = 0-0.5) ferrites with Bi2O3 sintering aid were prepared by microwave sintering method at a low sintering temperature of 870 degrees C compatible with low temperature co-fired ceramics (LTCC) systems. Detailed effect of La-Co substitution amount on their crystal structure and magnetic properties were mainly investigated. The results show that the pure M-type crystal phase is successfully obtained for the ferrites with La-Co substitution amount x not higher than 0.3. With further increased substitution amount, the multiphase structure is formed, where the non-magnetic alpha-Fe2O3 phase and LaCoO3 phase coexist with the M-type phase. Appropriate La-Co substitution improves the magnetic properties of the ferrites, including the saturation magnetization M-s, effective magnetic anisotropy constant K-eff, magnetic anisotropy field H-a, and intrinsic coercivity H-ci. Besides, the Curie temperature T-C of the ferrites exhibits a rapid decrease when the La-Co substitution amount exceeds 0.3. It is suggested that the La3+-Co2+ ions can partially substitute the Sr2+-Fe3+ ions for the ferrites, leading to enhanced magnetic properties. Typically, the obtained Sr1-xLaxFe12-xCoxO19 (x = 0.2-0.3) ferrites can provide improved M-s above 64 emu/g, H-a above 1510 kA/m, and H-ci above 330 kA/m as low temperature sintered M-type hexaferrites, which are promising for use in future design and realisation of self-biased circulators in LTCC systems. (C) 2015 Elsevier B.V. All rights reserved.